The present disclosure pertains to methods and compositions for preventing or alleviating the loss of drilling fluids, fracturing fluids, gravel packing fluids and other well treatment fluids into a subterranean formation during drilling or construction of boreholes therein.
In the oil and gas industry, a common problem in drilling wells or boreholes in subterranean formations is the loss of circulation of fluids, such as drilling fluids or muds, out of the borehole and into the subterranean formation during the drilling. Such lost fluids typically go into fractures or other openings that may be preexisting or possibly induced by excessive pressures during the subterranean operation.
A large variety of materials have been used or proposed in attempts to cure lost circulation. Traditional fluid loss materials are generally categorized as either solid materials or settable/polymeric materials. Traditional solid materials may be divided into three types or categories: fibrous materials, such as shredded automobile tires or sawdust; flaky materials, such as wood chips and mica flakes; and granular materials, such as ground nutshells. Settable materials include, for example, cement slurries, whose strength increases with time after placement. Polymeric materials include, for example, polyacrylamide dispersed in water that may then emulsify in a paraffinic mineral oil, typically using a polyamine as an emulsifier.
Another known example provides an improved lost circulation material that comprises a blend of a resilient, angular, carbon-based material and a water-swellable, but not water-soluble, crystalline synthetic polymer. Preferred carbon-based materials comprise resilient graphite carbon particles and ungraphitized carbon particles. Preferred synthetic polymers comprise polyacrylamide, and most preferably a dehydrated crystallized form of cross-linked polyacrylamide that will readily swell following exposure to water or aqueous based fluids. Such swelling may be delayed by salts in the water, such as the use of brine or addition of calcium chloride. However, these polymers have a soft consistency, and do not adhere to each other. As such, their ability to form strong barriers capable of preventing lost circulation is diminished.
Finally, gelling a treatment fluid using a polymeric material may be used to increase the fluid viscosity such that fluid loss is less likely to occur. In many subterranean operations the treatment fluid is not just gelled, but also crosslinked to further increase viscosity and reduce fluid loss.
Although many materials and compositions exist and have been proposed for preventing lost circulation, there continues to be a need for even more versatile and better compositions and methods for preventing lost circulation.